A liquid crystal display uses a backlight for lighting liquid crystal cells. According to the type of the liquid crystal display, edge-lit backlights have been employed for relatively small liquid crystal monitors, while direct backlights have been employed for relatively large liquid crystal televisions. As a reflective film for these backlights, a porous white film formed by air bubbles is commonly used (Patent Literature 1). There has been proposed a white film with an ultraviolet absorbing layer deposited for preventing yellowish discoloration of a film by an ultraviolet ray emitted from a cold cathode fluorescent lamp (Patent Literatures 2 and 3). Further, a reflective sheet in which a layer containing a soft bead is deposited on a base sheet layer has been developed as a product that is suitably used particularly with a prism-shaped light guide plate (Patent Literatures 4 and 5).
In recent years, however, edge-lit backlights have been employed even for liquid crystal televisions in association with thickness reduction of liquid crystal TVs, and development for edge-lit backlights has been vigorously conducted at the same time. Further, for reduction of power consumptions and freeing of mercury, light emission diodes (hereinafter abbreviated as LED) are being employed as light sources.
For a liquid crystal TV, unlike a notebook personal computer and a desk-top monitor, a high luminance is required and a large number of LEDs should be placed. Thus, it has been necessary to prepare a chassis using aluminum having a high heat conduction coefficient to take measures against heat radiation. However, employment of aluminum tends to result in poor mechanical strength. Thus, it has been necessary to form convexities and concaves on a back chassis 4 by drawing as shown in, for example, FIG. 4. The convexities and concaves have also been intended for saving space by placing circuits and the like in concaves 7 for thickness reduction.
For an edge-lit backlight, a light guide plate is absolutely necessary as an optical member. Concerning the light guide plate, a size of up to 25-inch type is sufficient for conventional notebook personal computers and desk top monitors, but a 30 to 60-inch type is required for TVs. Thus, light guide plates having convex portions with dot printing applied mainly on an acryl plate (thickness of 3 to 4 mm), light guide plates having concave portions by laser processing and UV transfer processes, and so on have been developed.